128 A. E. Verrill — Bermudian and West Indian Beef Corals. 



Plate XXV. Figures 2, 3. 



The Isophyllia rigida Verrill (Bull. Mus. Comp. Zool., i, p. 50, 

 1864) was based on Astrea rigida Dana (Zooph., p. 237, 1846). The 

 type of the latter is in the Museum of Yale University. It is a badly 

 beach-worn, astreiform specimen, with irregular polygonal calicles, 

 mostly 10 to 12 mm across. The walls are very solid, often 3 to 4 m 

 thick. The edges of the septa are entirely destroyed. In sections it 

 resembles an Isophyllia with unusually well isolated calicles. Its 

 origin is unknown ; West Indies? No. 4297. 



Several fresh specimens from the Bahamas (coll. Fv. P. Whitfield), 

 Amer. Mus. and Yale Mus., are apparently of this species. These 

 have deep, roundish or irregular, isolated calicles, 10-1 5 mm in diame- 

 ter ; many are dividing ; septa about 30, stout, exsert, strongly 

 spinose-dentate, the distal teeth larger, divergent ; upper ones erect, 

 prominent, acute; columella small, trabecular. Walls entirely united, 

 nearly solid. The larger hemispherical masses are 90-1 00 mm aero—. 

 No. 6616. Plate xxxiii, fig. 4. 



Allied to M. Harttii, var. conferta, but septa are thicker, with the 

 distal erect teeth much stronger ; walls more solid. 



Mussa Harttii Verrill. 



Mussa Harttii + Symphyllia Harttii Verrill, these Trans., i, pp. 357, 358, 1868. 

 B. Eathbun, Proc. Boston Soc. Nat. Hist., ii, p. 40, 1878 ; Amer. Naturalist, 

 xiii, p. 542, 1879. 



Plate XXII. Figures 1-2. Plate XXIII. Figures 1, 2. 



Plate XXV. Figure 4. Plate XXXIII. Figure 3. 



A larger series of this species than that first studied has convinced 

 me that both the forms originally described by me, provisionally, as 

 distinct, are really only extreme growth-forms of one variable species. 

 In the Museum of Yale University there are several intermediate 

 specimens, some of which I have now figured. (PL xxii, figs. 1, 2.) 

 It occurs with all the corallites united to their summits by a vesi- 

 cular exotheca (jSymphyllia-form, pi. xxiii, fig. 1), var. conferta; in 

 dichotomous groups with the calicles and branches disunited, and 

 without exotheca (fig. 2), var. laxa : in masses with the corallites free 

 for only a short distance, leaving o\\\y deep grooves between (pi. xxii, 

 fig. 1); in groups in which the corallites are free for \ or ^ their 

 lengths, with exotheca below (fig. 2), var. intermedia ; and in various 

 other intermediate forms. 



One specimen (pi. xxxiii, fig. 3) consists of a cluster of seven 

 calicles of the Symphyllia-iorm, arising from a dichotomous branch 

 of the typical Mussa-iorm.. No. 4545. 



